diyAudio Forums Archive - Where do we most often fall short with amps?

diyAudio Forums Archive > Top > Amplifiers > Solid State

Where do we most often fall short with amps? - Click HERE for Original Thread

walker

Some homebrew amps do perform as well if not better than the high end manufacturers products. But in my experience many fall short, often without the builders being aware. No I do not make them aware if the short commings as a rule, I sometimes suggest improvements though:)
Where do you think that DIY amps most often fail to perform better than they could, or where should we be concentrating more effort?

I'd be greatfull for you experience.

Enjoy the music, take care, regards, WALKER

MikeW

I think the biggest problem for the DIY is the housing and hardware. Except for Peter. Heatsink are always hard to get. The electronics are the easy part. There are alot of good proven designs to build thanks to Nelson Pass, Rod Elliott, Hugh Dean just to mention a few.

walker

How much do the chassis and heatsinks effect the performance?
Certainly a poor enclosure can cause shielding and grounding problems.
The heatsinks apart from size, how else do you think that they effect the output?

Take care, enjoy the music, regards WALKER

Jean

I agree with MikeW, and would like to add physical layout and relative location of psu components to the list too. Thats just from my personal experience of course :)

dutch diy

Probably each DIY at some point bends one or two rules related to "safety" when using mains-power, although no serious hazards will occur from that.
:headbash:

Christer

quote:

Originally posted by dutch diy
Probably each DIY at some point bends one or two rules related to "safety" when using mains-power, although no serious hazards will occur from that.
:headbash:

Most certainly a number of DIYes over the years went listening
to heavenly music sooner than expected because of that. :RIP:

However, it probably will not be a problem for the sound quality
in general, rather, some most likely bend the rules deliberately
for the reason of improving the sound.

pinkmouse

quote:

Originally posted by Christer
However, it probably will not be a problem for the sound quality
in general, rather, some most likely bend the rules deliberately
for the reason of improving the sound.

And what is the point in having the most wonderful sounding system, if you, or someone close to you dies because of it...:(

Christer

quote:

Originally posted by pinkmouse

And what is the point in having the most wonderful sounding system, if you, or someone close to you dies because of it...:(

Yes, and that was meant to be implicit in the what I said, in
case somebody missed it.

:att'n: Never compromise safety, especially regarding the mains
voltage circuitry :att'n: (says one who hasn't always lived up
to that in earlier projects, but I do intend on improving in that
respect.)

Actually, this is also an important thing to think about if you
build equpment for friends or sell equipment. It's one thing
if you endanger your own life, but most of us would probably
find it even worse if someone else dies because of an amp
we have designed.

pinkmouse

I think one of the things we miss out on is being able to compare different iterations of designs against each other.

I remember Jonathan Carr stating that he would have four or five versions of his products, each with slight changes, on the go at once, so he could check components and layouts very easily for any improvements or degradations. This isn't so practical for the DIYer, unless you're building something cheap and easy like a GainClone.

walker

I have seen a few cases where the amplifier earth was disconnected from the mains earth to cure hum problems; this is of course a dangerous habit.
I had one system brought to me to fix the mains hum. I couldn’t find any problem with the amp and had to travel to the owner’s house to check the installation. I found the main earth connection on the house had been disconnected! Even worse, the connections on all the company owned houses in the street were in the same condition, (we use an MEN, Multiple-Earth-Neutral system here). The local supply authority inspector, a good friend of mine, chased down the cause. A young and over zealous painter had just finished painting all the houses in the street, it was his job to paint the exteriors, the older painters did the insides as they were all air-conditioned. The young painter had disconnected the earth wire from the metal pipe to do a good job. A few of the residents had noticed a tingle when touching the taps but had though no more of it!

If you have a problem with noisy earths get them checked, don’t remove the symptoms, fix the problem before some gets killed. I have even heard of a local salesman suggesting that people cut off earth pins to “fix” the problem, don’t do it!

Having said that, circuit arrangement within the chassis, earthing and cable routes are common reasons why our DIY amps some times play their own tune. I agree with that!

Take care, enjoy the music, regards WALKER

thylantyr

Where do you think that DIY amps most often fail to perform better than they could

Lack of funds for the project ;)

Then compromises are made to
compensate.

Christer

quote:

Originally posted by walker
I have seen a few cases where the amplifier earth was disconnected from the mains earth to cure hum problems; this is of course a dangerous habit.

And some of us live in countries where we don't even have a
chance to connect the case to the mains earth since the wall
outlets usually do not have a mains earth. :(

Sandy H.

If the quality of parts is to be considered important (which it no doubt is) and if even the combination of said parts is critical, it seems that short of copying directly an exact design from a manufacturer, down to the part number, there could be degradation. I personally have trouble convincing myself to buy a single 'brand Y' resistor from one place and a special capacitor from another. Many of my projects are behind as I refuse to place a $3 order to anybody, and if Digikey has one part and Mouser has the other, I wait until I have enough parts to order from each prior to placing my order. My gain clone project is on hold for a 4.7uf cap, and is likely to be for a month, especially if I use an esoteric vs. Xicon. And in the end, I am never likely to hear a Gain Card or even another gain clone to compare to.

To sum up, if the results of DIY are sometimes compromised, I'd suspect the order of cause is: ignorance (which part/layout/etc is most critical), financing (spending the right money in the right places) and sourcing. After that, I bet any dedicated hobbyist could eventually beat the quality of the physical assembly.

Thanks for the chance to discuss this subject.

Sandy.

jcarr

Rather than thinking of where you are lacking compared to commercial manufacturers, wouldn't it be more productive to carefully consider your own specific design and manufacturing environment, and come up with audio designs that utilize the resources that you presently have to the fullest extent possible without overwhelming them?

Once you are satisfied that you are extracting the most possible from your present resources, the next step would be to conduct your own assessment of the areas in which your present resources are a limitation, and then devise ways to extend beyond those limitations. For example, if you don't have the ability to come up with unique but capable schematics, either study your butt off (always a good idea), or enlist the aid of a good schematic designer who can cover up for your inadequcies. If you can't design high-performance pcb layouts, again study, study, study. OTOH, book knowledge is no substitute for hands-on experience, nor can it replace clever insight and imagination.

Never forget that the schematic is an abstract and simplified version of the "real" schematic, which is determined by the board layout, componentry choice and overall physical construction. In other words, the schematic, board layout and physical construction should be revised flexibly so that what is on the board and the physical construction is as close to what is in the schematic as possible.

And if you can only make single-layer pcbs, start searching for a professional board house who is willing to make multi-layer boards in small quantities.

Regarding componentry, although a good range of high-quality active devices is important, I don't think that the choice of passive componentry is nearly as important as many audiophiles appear to believe. Using only standard electrolytics, motor-grade film caps, industrial SMD caps and metal-film resistors, as long as the schematic, board layout and physical construction are designed really well (which I admit is partly a personal evaluation), you should be able to make a design which beats the pants off 75% of all commercial designs. Componentry can be a bonus, but it can never be a replacement for good basic design.

Everyone - commercial manufacturer or amateur designer - has to start from somewhere. I know that the designs that we were doing some 16 years ago were very much less ambitious and capable than our present products.

I think that the main points are to have a general idea of what direction _you_ want to go in, understand where you are weak - the areas that hamper your progress in the direction that you wish to go in - and then set about resolving those weaknesses. No need to hurry or make haste - steady, consistent progress over time will do the trick nicely, IME.

hth, jonathan carr

Christer

Jonathan,

Excellent suggestions and comments.

You do actually also touch one thing I have intended to ask
about on the forum sooner or later, so why not now? Could
you, or somebody else, point to some good resources
(preferrably on the web) about rules/guidelines for how to
do good PCB layouts? I could come up with a few things that
seem intuitively reasonable to me, but they may be wrong
and are by no means sufficient. I have tried to search the
web but everything I found seemed to be about how to
use various layout software, which is not what I want.

EC8010

quote:

Originally posted by jcarr
And if you can only make single-layer pcbs, start searching for a professional board house who is willing to make multi-layer boards in small quantities.

Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.

Christer

quote:

Originally posted by EC8010

Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.

Speaking of layers, people very often seem to favour the use
of ground planes, which may be sensible for digital designs,
but is is generally a good idea for analogue considering the
extra parasitic capacitance we get?

EC8010

Hello Christer,

oh yes. Ground planes are a super idea. Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise.

jcarr

Christer:

>Could you, or somebody else, point to some good resources (preferably on the web) about rules/guidelines for how to do good PCB layouts?<

Whatever you do, don't study the board layouts used in the vast majority of audio designs (including most commercial products), because as a general rule, they aren't very good. IMO, IC designers and IC applications engineers have a much better handle on good pcb layout practice.

Most of my library is in printed form (and a great deal of it is in Japanese :)), but here are some starters on the web.

http://www-s.ti.com/sc/psheets/sloa089/sloa089.pdf

http://www.analog.com/UploadedFiles...08865AN-202.pdf

http://www.linear.com/pdf/an47fa.pdf

http://www.old555.com/LPE/DaEtiCsuiPitdcrut.html

Burr-Brown also used to have some _very_ nice papers on system board design, (they looked like PowerPoint slide presentations), but after the merger with TI, I haven't been able to locate any URL. I may have them in some form somewhere, but I won't make any promises.

But any paper that you read is only a starting point. It is up to you to study it, digest the contents, mull over the implications, and come up with your own design approaches. Things that I now automatically consider include, total surface area and the sensitivity of the circuit as an RF antenna, trace inductances and capacitances and their effect on circuit performance and stability, common-impedance errors, noise coupling, ground and power planes, ground currents, node impedances, leakage currents and the desireability of guard rings and isolated stand-offs, and on and on.

hth, jonathan carr

quote:

oh yes. Ground planes are a super idea. Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise.

What do you think the tradeoffs are between ground planes and putting some bandwidth limiting at the input to keep the RF out in the first place?

jcarr

EC8010:

>Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.<

Although I agree that in many cases it is better to avoid the auto-router like the plague, designing for one layer only isn't a worthwhile priority, IMO. Although my circuits tend to be fairly complex affairs as far as audio designs go, usually there will be circuit nodes that benefit from the impedance control to be gained by intimate proximity to a ground or power plane. If parasitic capacitances are detrimental to a given circuit node, open the ground or power plane in that locale only.

Compared to designing 2-dimensionally with a single-layer PCB, designing quasi 3dimensionally with a multi-layer PCB is far more likely to get you a compact circuit that has smaller antenna area and therefore less sensitivity to RF pickup. Besides, 4 or more-layer PCBs allow you to do various tricks that would be impossible with a double-sided or single-sided PCB, unless you don't mind _lots_ of jumpers (been there, done that).

That circuit may not _need_ more than one layer, but it will probably measure and sound better with a more sophisticated board design.

SY:

>What do you think the tradeoffs are between ground planes and putting some bandwidth limiting at the input to keep the RF out in the first place?<

I do both.

hth, jonathan carr

alvaius

I have had a chance to review a lot of designs at the PCB level. There are many many cases where a GROUND PLANE IS NOT a good idea, especially for audio circuity. When you have a ground plane, you have very little control over where the current flows, hence you can get current flow from your high current outputs into your low level inputs. In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.

Digital of course is a whole nother matter where the primary goal is power supply stability at the IC pins, controlling impedances, etc.

Of note, improper use of power and ground planes can even contribute to radiated noise.

Alvaius

usekgb

One thing I have noticed in a lot of commercial designs is poor power supply design. They can almost always use improvements. All too often, the supply caps are too small, the bridges can't handle enough current, and mosfets aren't able to dissapate enough power. 90% of the amplifier and electronic repairs I do are power supply related. I have seen more power supply caps that have exploded than I can count.
One thing we can learn from this is to try and engineer everything to handle any power load we may throw at it. I like to over-engineer my power supplies if I can. For example......Use caps that can handle higher voltages than the circuit needs. This will help if you have any power surges or unusually high current draws from your supply. This goes for the rectifiers as well. Go ahead and use rectifiers that are over rated for your aplication.
These are just my thoughts on the subject. I hope this helps.

Cheers,
Zach

jonathan, thanks. So would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?

Shaun

quote:

When you have a ground plane, you have very little control over where the current flows, hence you can get current flow from your high current outputs into your low level inputs. In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.

The thing to note here is that there are two grounds: signal ground and power ground. Don't mix them up, and you'll avoid this problem. Inevitably they need to get connected electrically, but this should be done at a single point on the board, away from heavy current paths. It is still possible to have a star point with copper floods on the board (and you aren't limited to just one).

On another point, one of the constraints (money) often makes it impossible to have multiple development iterations of boards, so we try to do it best first time around. An inexperienced builder, could be forced into overcomplicating the design because of trying to get all the best goodies in at once. Rule here is to keep it simple, and grow slowly, steadily gaining confidence (OK, I know I'm just repeating here what someone said above...)

Christer

Jonathan,

thanks for the links. I had already read nr. 2, that's a good one.
I just has a brief look at the first one, and it seems quite
useful too.

I am afraid your japanese texts wouldn't be of much help to me.
Although I did take a short course in Japanese a few years ago,
just out of curiosity about the language, I didn't get very far
and I don't remember more than a few useful phrases like
"watashi no atarashi jidoosha akai" :) (which I probably
don't remember correctly anyway and besides, my jidoosha
is shiro not akai). It's an interesting language,
though, which I wouldn't mind learning more about if I only
had the time.

jcarr

Alvaius:

>When you have a ground plane, you have very little control over where the current flows<

On the contrary, it is feasible to analyze the grounding and locate the circuit nodes that tie into the grounds in a manner that allows for rather well-controlled ground currents.

>hence you can get current flow from your high current outputs into your low level inputs.<

The most basic precaution that you can take is to keep the power and signal grounds separate and tie them together only at one point. With multilayer circuit boards, it is just as easy to star planes as it is traces.

>In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.<

Naturally, the designer should study, measure and think carefully before he does anything. "Just do it" isn't good enough. For low frequency applications, starring traces is usually sufficient, but for wider bandwidth designs, I would recommend starred planes, or combining starred traces and planes.

My designs also incorporate active grounding (discrete circuits which accomplish similar functions as the TLE2426), which allows me to take care of many grounding requirements while simplifying the currents flowing in the grounds.

>Of note, improper use of power and ground planes can even contribute to radiated noise.<

No doubt. Incompetent use of anything can cause problems, but more often than not, the problem lies with the designer, not his tools.

hth, jonathan carr

jcarr

Sy:

>Would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?<

Oh yes. Planes and striplines in P2P are an iffy proposition at best :). And multilayer PCBs allow you to deal with relatively complex circuitry that would drive you batty if you ever attempted them in P2P.

But PCBs also have drawbacks, including problems with high-impedance nodes and leakage currents, and only two surfaces for installing parts. This is why in my own designs, multilayer PCB layouts with comprehensive ground and power planing serve as the foundations, but these are then augmented with component and board stacking, localized P2P, guard rings, floating isolater pads, teflon-insulated standoffs, clover-leaf terminals, and various other structural go-faster tricks.

regards, jonathan carr

Bas Horneman

Most DIY'ers (and Pro's) mostly SS I think fall short in the PSU department. Using SS diodes with huge caps right behind them.

http://www.nutshellhifi.com/library...Fest_Talk2.html (bottom part)

I am assuming that Lynn Olson is right here. And my gut says he is.

Cheers,
Bas

EC8010

jcarr, what I was getting at, in espousing single-layer boards, is that many PCBs have longer, more convoluted tracks, and links than necessary, but single-layer design forces you to think hard. Of course, from a point of view of design efficiency, the time required to achieve an ideal design is not worthwhile - there's a parallel here with computer code.

SY, aren't input filtering and ground planes two different issues? Ground planes help us to avoid local noise, and input filtering assumes that we picked up noise on the incoming cable.

In case anyone here thinks I'm in the business of teaching grandparents to suck eggs, I only stuck my oar in because I've had disappointments caused by "professional" PCB designers. The best example was when I allowed my boss to persuade me to let a PCB designer take my circuit and implement it. The (digital) circuit compared the timing of two video signals in three stages of severity. It worked on breadboard (even the 4.43MHz phase comparator), and it worked on wirewrap. The first PCB couldn't even manage the middle stage test. (The electrical connections were fine, and it matched the circuit diagram, but the poor layout stopped it.)

Everyone else has now said all I want to say about PCBs. Good layout is an art, and is driven by many (and conflicting) rules.

Jocko Homo

A ground plane can turn out to be good antenna, both for transmitting and receiving.

Biggest problem that we ever had, was filter caps. They all sound different, different enough to really screw up an amp if you pick the wrong ones. Too big, or too small, can mess things up. Even picking the wrong style can be a mess.

We never had enough time, or money, to source every possible type available. Sometimes the best ones were not availble unless we bought more than we could use.

Wish I could give a definite answer on how to do that, but that was one problem we never had a handle on. Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.

Jocko

ALW

Any design is only ever going to be as good as it's weakest link, and it's therefore impossible to make generalisations.

I agree though with everything Jonathan has said. In audio details matter, a lot.

So many problems are simply a matter of assuming that it doesn't matter, when in fact were you to perform an error budget and work it out, it often does. Bear in mind errors occur in many domains too.

Tiny errors, in the order of uV make differences, much of audio is simply about reducing errors, so reading about precision design (which is often of a DC nature) then applying it to AC design makes for big differences.

No magic PCB or universal panacea applies, but to really be sure of the improvements you make stick with a design and find it's limits / limitations.

So many here build a multitude of different circuits / topologies but never optimise any. Build a design, listen, measure then build another.

Now you can iteratively improve the design, always with reference to the last. It's time consuming, but really worth the input in my experience, and you always have a reference to refer to - none of those 'I think it's better' changes.

You will be astonished with the magnitude of improvements you can get from this approach, but choose the initial design carefully, some are VERY hard to get working properly.

Final tip - ignore most of the published audio reference work, it will tell you far less than a good detailed scout through the semi-manufacturers online (and free) libraries. There's a few exceptions to the above, but not many.

Above all have fun, when you get it right, there's no better feeling in the world (and it will also give you far greater insight into the price tags charged by comercial companies too - there's a lot of labour involved in good audio design).

Andy.

P.S. the current flows in a ground plane are highly predictable - remember current flows in loops - analysing those loops is a crucial bit to getting it right.

ALW

In addition to the above, the circuit elements you can't see on the schematic often dominate the ultimate performance of a circuit (as alluded to by Jonathan's post).

To get a real handle on this, redraw your schematic showing all junction capacitances, non-ideal component characteristics, trace inductance, C etc.

For a first iteration, just the semi's junction C's and maybe cap's non-ideal parameters will tell you a lot.

Now analyse the effect of every one. Dealing with these, through component choice, topology etc. often brings REALLY BIG rewards, definitely bigger than fiddling with audio-grade components in non-optimal designs will, and it's cheap - a big benefit for skinflint DIY'ers like me ;)

Once those bits are sorted, then you get to the minutaie of components, where the audio-grade bits have a part to play.

Andy

janneman

quote:

Originally posted by jcarr
Sy:

>Would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?<

Oh yes. Planes and striplines in P2P are an iffy proposition at best :). And multilayer PCBs allow you to deal with relatively complex circuitry that would drive you batty if you ever attempted them in P2P.

But PCBs also have drawbacks, including problems with high-impedance nodes and leakage currents, and only two surfaces for installing parts. This is why in my own designs, multilayer PCB layouts with comprehensive ground and power planing serve as the foundations, but these are then augmented with component and board stacking, localized P2P, guard rings, floating isolater pads, teflon-insulated standoffs, clover-leaf terminals, and various other structural go-faster tricks.

regards, jonathan carr

Jonathan (and ALW), thanks for all the inside tips from your posts. They all seem so logical, but it always does in hindsight. In the exitement of the moment, it is good to lean back and go through the mental checklist of all the important issues. It seems that this is necessary to get a real good design out. Like Andy says, you need to dig in deep to really understand your design, only then can you progress.

One advantage of a double sided PCB I haven't seen noted is the fact that it makes it easier to keep a design compact without long looping traces (compared to a single side design). That for me makes it worth while, even without the ground plane options.

In the initial design of a PCB I often use the auto router to verify optimum placing of components. It's a bit easier than using the ratsnests, at least for me. But then I delete all routes and do it manually, starting with sensitive and/or input lines to keep those compact, then the PS decoupling caps, keep them close to where they are required, then the rest. Then leave it for a few days, then look at it again. Often I need many iterations, including some major repositioning of components, before I get it to my liking.

Jan Didden

jcarr

Jocko:

>A ground plane can turn out to be good antenna, both for transmitting and receiving.<

Absolutely. And in general, ground in an amplifier is one of those fictional abstractions that is only as real and reliable as the designer makes it.

>Biggest problem that we ever had, was filter caps.<

I try to design so that any capacitor will operate in either constant voltage conditions or constant current conditions, but not both at the same time. I find that doing this won't altogether eliminate the sonic fingerprint of a capacitor type on a circuit, but will reduce it considerably.

>Sometimes the best ones were not availble unless we bought more than we could use.<

IME, this is a more common occurance than "sometimes". The minimum-order policies for special or custom capacitors varies according to the manufacturer, but the sums and quantities are never piddling.

>Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.<

Different board layouts and physical constructions can also affect the sound to a surprising extent. Keith Herron mentioned to me that for some of his products he spent over a year iteratively designing board layouts and measuring and listening to them before he was satisfied.

regards, jonathan carr

jeffreyj

quote:

Originally posted by EC8010
Hello Christer,

oh yes. Ground planes are a super idea. Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise.

Weeeelllll... perhaps not. Letting the ground plane get too close to the inverting input of a differential amplifier (discrete or op-amp) is not such a good idea, for one example - the capacitance introduces a destabilizing phase shift.

Also, ground planes really only shine at audio frequencies when the node impedances they surround are low! High node impedance = high signal rolloff due to the shunt capacitance.

In my experience, ground planes are really best suited for high speed digital and RF circuits, where all node impedances are either low or tightly controlled.

'Course, a well-designed ground planed board will likely beat the pants off of a poorly designed plain board any day of the week, which is why I qualified this whole reply with "perhaps" right there in the beginning!

;)

quote:

SY, aren't input filtering and ground planes two different issues? Ground planes help us to avoid local noise, and input filtering assumes that we picked up noise on the incoming cable.

EC, I was responding to your statement, "Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise." That kind of issue, I think, is amenable to input filtering.

jonathan, I'm fairly familiar with the techniques you've outlined (I've even used them in my non-audio products), but I've seen people in this forum claim that p-t-p is much superior sonically. Now, in my audio gear, I normally use p-t-p, but that's because I build one-offs, you know, DIY, and have to watch the dollars. With no cost constraints, I'd use PC. The claims of p-t-p superiority don't make much sense to me, but as I haven't tested this myself, I thought I'd take the opportunity to ask someone who has. Domo domo.

jcarr

SY:

>I'm fairly familiar with the techniques you've outlined (I've even used them in my non-audio products)<

Very interesting! So you have made commercial products that incorporate localized P2P, teflon standoffs, clover-leaf terminals and what-not? May I ask what type of products these were? I know of companies that utilize these techniques for prototypes and really small-scale runs (and I have seen the guts of some missile onboard radar systems that were built similarly on stepped teflon-over-machined metal "pcbs"), but I don't recall seeing any modern commercial products that used such techniques (perhaps some of the older Tektronics test gear would be somewhat similar).

>The claims of p-t-p superiority don't make much sense to me, but as I haven't tested this myself, I thought I'd take the opportunity to ask someone who has.<

For certain things, P2P can be decidedly superior. If you consider a high-impedance gain node, the impedance that you can get on a pcb is usually limited by the board material and construction (Japan and much of East Asia has a very humid climate, which makes matters worse). If you make that same node as a dead-bug P2P structure, the limitation is more likely to be the Early voltages of the active devices.

OTOH, design is all about goals and priorities. While I reckon that P2P can be superior for certain tasks, right now I am mostly interested in developing topologies to obtain superior performance and sonics. And many of those topologies are complicated enough that you wouldn't want to execute them as P2P. In the future, if I become interested in simpler topologies once again, at that time I may want to consider using P2P more extensively.

regards, jonathan carr

jonathan, my more exotic work was in aerospace and instrumentation (electrochemical, spectroscopic, data acquisition, FT methods). More prosaic work in computer peripherals, where I became VERY familiar with environmental demands in Southeast Asia. Now I do wine corks. Sic transit gloria SY.

Christer

Since I asked about PCB layout issues earlier, I just want to
pop in here and say that I have found the discussion on this
very interesting and enlightening. Still have to read up a bit
to understand all the issues on groundplanes, though, but
there has been quite some useful stuff said.

dutch diy

quote:

Originally posted by Bas Horneman
Most DIY'ers (and Pro's) mostly SS I think fall short in the PSU department. Using SS diodes with huge caps right behind them.

http://www.nutshellhifi.com/library...Fest_Talk2.html (bottom part)

Hi Bas,

I totally agree to the observation about lack of regulated output stages.
I also know the reason for this as, with SS amps, powerfull output stages require currents and voltages which are beyond limits of commercial available voltage regulators.

The alternative: building a regulated powersupply from discrete components is not a complex task. The result however would
a: increase the part count dramatically (for each 1 - 2 ouput devices there should be an regulating device roughly)
b: increase the amount of heat which needs to be dissipated.

For my simple JLH-amps I stick to fully regulated powersupplies.

I design the single sides PCB's from my basic set of rules just using Corel-Paint and my gut-rules:
-layout should reflect the circuit diagram;
-avoid long traces;
-keep high-current traces short and wide;
-use the physical dimension of the components to cross other lines. (I personally use resistors for this, and make sure that the resistor is not mounted flat to the board where there is a crossing),.
and NO SQUARE's on edges as this seems to be more vulnerable.

jos

fdegrove

Hi,

Hats off to you, Jos.

Bas already knows I am a big fan of regulated supplies and I would point to the PSU as the main part were most manufacturers try to save bucks.

It certainly is my experience that almost any commercial amp can be improved by either beefing up the PSU or adding regulation.

The latter is 9/10 almost out of the question on commercial designs due to lack of voltage headroom unless you make on outboard supply.

Thing is, not many people are knowledgeable about regulators though, neither with valves nor transistors.

In the age of digital hash pollution they deserve a huge welcome.

More later perhaps, ;)

EC8010

Hello Frank,

trouble is, regulators aren't terribly good at dealing with RF hash. Jolly good otherwise, though. If they can be protected from the RF racket, then they're good. But, as you point out, they cost almost as much as the audio amplifier, and (being single-ended) they're harder to design for low distortion under varying current.

Christer

quote:

Originally posted by EC8010
Hello Frank,

trouble is, regulators aren't terribly good at dealing with RF hash. Jolly good otherwise, though. If they can be protected from the RF racket, then they're good. But, as you point out, they cost almost as much as the audio amplifier, and (being single-ended) they're harder to design for low distortion under varying current.

RF hash, ground planes and a lot of other interesting stuff is discussed in the folloing excellent paper
http://focus.ti.com/lit/misc/sloa089/sloa089.pdf
that Jonathan recommended earlier in the thread. I'd say this
is highly recommended readin on PCB layout for those, like
me, who do not alraeady know how to get things right (got
the time to read it today).

EC8010

Hello Christer,

that's a cracking chapter (he uses the get-out "beyond the scope of this book"), and I've saved it ready to print later for more considered digestion. I'll be looking for the book next.

What I was actually getting at was a much simpler limitation. All regulators are fundamentally an op-amp, a voltage reference, an output sampling element, and a power regulating element. Because of this, they suffer from the fundamental limitation of any op-amp. They have a finite gain-bandwidth product, which is further compromised by the power regulating element. As a consequence, their noise rejection falls with frequency, and it's usually pretty poor by 10kHz, let alone RF. This applies whether the op-amp in question glows in the dark, or is this month's wonder op-amp, just a matter of degree. So they all need protection. But you knew that..

jcarr

Dear Christer:

I tend to re-read certain papers before starting any new schematic or board design, and SLOA-089 is one of them. Nearly all of the concepts mentioned therein are things that are simple, obvious and should be committed to heart, yet being exposed to the occasional reminder is never a bad idea.

I think that you will also find it useful to have some knowledge of guard ring concepts. Audio amplifiers are essentially analog calculators, and methods that can reduce measurement and calculation errors are invariably worth implementing.

http://www.ce-mag.com/ce-mag.com/ar...0103CE_028.html

http://www.quadtechinc.com/resource...estfixtures.asp

hth, jonathan carr

Fred Dieckmann

The reference:
http://www.ce-mag.com/ce-mag.com/ar...0103CE_028.html really refers to digital design and may be contrary to the best strategies for analog circuits. It was really too brief and general for much insight into EMI and signal integrity. I would dig around at the links section of www.sigcon.com for resources on the subject of board design for EMI reduction. I have several reservations about guard rings. Most of the real applications or guard rings that I have seen were to keep DC leakage currents for introducing DC error terms into high impedance DC coupled circuits. The introduction of increased capacitance at the inverting input can cause problems. The capacitance at this node is usually best made very small for high bandwidth devices an circuits. The usual mistake I see is excessive lead lenth between this node and the junction of the feedback resistors that connect to this node. Keep this connection as short and small as possible is one of the highest priorities in layout of an analog amplifier/preamp circuit. Try and design guard rings for a surface mount op amp so typical these days and you will see what I am going on about. I have had very fast op amps work better with the inverting input pin bent up off the PCB and the resistors soldered to it with minimum lead length. This made a big sonic improvement on a diffential op amp buffered S/PDIF digital input and was a pain to buld in prduction but worth the sonic benefits.
One of the best resources on grounding and layout for analog is

http://www.analog.com/UploadedFiles...08865AN-202.pdf

which we have both posted the link to before but is worth doing again.

This one, High Speed Amplifier Techniques by Jim Williams at Linear Technology, will change your life and is one of my favorite ap notes ever:

http://www.linear-tech.com/pdf/an47fa.pdf

jeffreyj

quote:

Originally posted by Fred Dieckmann
... I have several reservations about guard rings. Most of the real applications or guard rings that I have seen were to keep DC leakage currents for introducing DC error terms into high impedance DC coupled circuits. The introduction of increased capacitance at the inverting input can cause problems.

Amen to that. Guard rings are for things like pH meter amplifiers - zero ac bandwidth needed and input imedances that won't load down a 100+ megohm electrode.

quote:

This one, High Speed Amplifier Techniques by Jim Williams at Linear Technology, will change your life and is one of my favorite ap notes ever:

http://www.linear-tech.com/pdf/an47fa.pdf

Amen to that, too! This is by far one of the most comprehensive references on op-amp application ever written. I've printed it out 3 times because it keeps falling apart from use! What a gem!

traderbam

quote:

Walker wrote: Where do you think that DIY amps most often fail to perform better than they could, or where should we be concentrating more effort?

Good question. Lots of good stuff written already. Some of my favourite pitfalls are:

1) Assuming wire/pcb traces have zero impedance
2) Assuming semiconductors behave like the "typical" figures in datasheets
3) Ignoring parastics (datasheets don't tell the whole story)
4) Forgetting that currents flow in loops (at audio frequencies)
5) Inadequate consideration of non-linearities and their effects
6) Thinking you can hear above 20kHz
7) Inadequate performance measures/unreliable test methods

Item 1 leads to many problems, especially in high feedback designs, and has been highlighted in the discussions on ground planes vs point to point. Item 2 is a really easy trap to fall in to, many people don't realise the parametric spread in semiconductors even between two devices with identical part numbers. ALW mentioned item 3. Item 4 has been mentioned and should be considered at the same time as item 1. In my experience item 5 is woefully neglected in most press and "expert" websites and is often swept under the carpet and almost never measured intelligently. Item 6 is a common misunderstanding - it is my way of combating the wide-bandwidth is ALWAYS better club. Honestly, you cannot hear above 20kHz. Item 7 is the very most neglected area and is one way I use to judge waht "experts" expound upon. If they say "x" is better because it is made of gold leaf from the mines of Solomon I ask "why?" and "how did you measure the improvement?". The why is usually not explained convincingly and the measurement process is often ill-conceived.

A few amateurs do manage to bridge these pitfalls and make really great sounding amps.

ALW

quote:

5) Inadequate consideration of non-linearities and their effects

This one is worth highlighting again and sits nicely alongside 'the components you can't see on the schematic' theme.

Not only do they vary between devices, but vary in the same device, in a non-linear fashion, dependant upon operating characteristics.

Also, understand the limitations of the components - those data sheet specs for that op-amp for example look marvellous, but try driving a capacitive / low-impedance load with them and many fall apart, primarily because their output stages are mostly ****. You won't get this info from your spice modelling either, because the output stages aren't modelled (in most cases).

Deal with this though, in terms of the load the op-amp sees and often things are often transformed!

Some simple pre-testing of components such as these can reveal loads of useful data.

Andy.

P.S. I really like no.1 above - most engineers I meet seem to think room temperature superconductors exist, in the form of PCB copper traces :)

mikek

quote:

Originally posted by jcarr
Dear Christer:

I tend to re-read certain papers before starting any new schematic or board design..

Amen!...fred diekmann take note!:)

mikek

quote:

Originally posted by jeffreyj

Amen to that. Guard rings are for things like pH meter amplifiers - zero ac bandwidth needed and input imedances that won't load down a 100+ megohm electrode.

[b]

Amen to that, too! This is by far one of the most comprehensive references on op-amp application ever written. I've printed it out 3 times because it keeps falling apart from use! What a gem!

Had mine printed double sided...and properly bound:)

Christer

I would just like to thank for the references supplied by
Jonathan and others. I have only had time to read the sloa-89
so far, and I had already read the an-202. I find them both
excellent reading and highly recommendable, also from my
non-expert point of view. To anybody who hasn't yet read them,
do so! YOu won't regret it.

It is intereting, BTW, that while there seems to be frequent
controversies on this forum, and similar ones, about whether
RFI is a big problem or not for audio gear, sload-89 which is
not in any way focussing on audio in particular seems to state
clearly that RFI is important to consider also at audio frequencies.

MBK

I think many shortcomings in DIY design are even more basic. I see three main problem areas, at least for myself:

1 - lack of breadth in theory and in experience. What I mean is this: a professional designer had to learn all the theory at least once, even the parts he didn't like, and design a lot of stuff that probably wasn't his pet project aither. Result? A lot of related nackground that is there as a diffuse library of knowledge to solve problems.

The average DIY'er has a good to very good (read: deep) knowledge of some isolated issues. Some are into capacitors, some into cables... and some have extremely good understanding of the spotlights in their interest. Still they often seem to lack a good comprehensive view of the whole, of what's most important and what is not, etc. Plus, most DIY'ers including myself naturally pick the areas they like most and ignore the rest. Then they fall short when they encounter a problem that needs a broader insight.

It can be as simple as finding a formula for a filter or recalculationg a modified design. I have done complex math in high school but didn't particularly like it. Now I am too weak in math to catch up with the application notes: the author usually assumes you know all the basics! Most DIY'ers don't. I don't. Not to mention the routine of buying a product and replacing selected parts of a carefully designed circuit with "better" parts of radically different specs (op apms with 10x speed...). Ugh.

2 - Secondly, as said before, measurement and calibration are often rudimentary. Example: I don't have a scope, a frequency generator, or a frequenzy analyzer. Not even a variable bench supply. Just a DMM and a fast peak meter, which can be a good enough crutch sometimes. That's good enogh for the initial simple copies of published designs. Once you want to create something a bit more complex however, you need more or it leaves you guessing in the dark even where you suspect problems for a good reason. But I don't have the instrument to verify my problem theory in a minute. All I can do is resolder the circuit and see if "it's still there". Sigh. Again it's a dollar problem for once, but you must also know what to measure and how! Not trivial.

Iam a scientist in a non electronic field :-) ... and I know for sure that the hardest problem is often just what to measure and how to do it.

3 - Finally, layout problems. Even a finished, published design can vary a lot depending on how you build it. This has been covered before in this thread and I second that.

One anecdote on that. I built chip power amps a few years ago and use them til today. Ah nowadays they are called Gainclones, nevermind. The past weeks I became quite unhappy with the performance that had seemed good so far. Well, I just knew it sounded bad, not why, and it was insiduous: zero self noise, zero hum, zero nothing, but clearly distorted on certain musical passages. Just the thing to drive you nuts. So I checked the whole DIY eqipment, everything, connections, solder joints, grounding, installed RFI filters (Christer, they still seem to work OK! - but that wasn't the problem after all), uncovered and corrected a few errors I had made , and all this improved the sound somehow. But it did not really fix it for good, or not well enough. Finally I check the main PSU I hadn't touched in 2 years. What do i see? I had connected the ground lead the wrong side of the filter caps, plus on a terminal strip rather than soldered between the main caps.

Well, fixingt this did more for the sound than anything else. This really was the main problem. There still is room for improvement and now I know where - it's all in the PSU department - but these 2 excess inches along a string of 14 ga wire made the difference between annoying transient ringing and a quite natural sound. So natural that after the 20 min resoldering job I spent 3 h listening to some of my less-frequently-listened-to-CD's. I had not done this in weeks because it sounded so annoying. !!!! .

Or in short: many circuits are fine. But the physical layout will make or break them, even in a PSU with, what, 6 (six) components all in all, transformer, rectifier, 4 caps. And here you need experience or a good teacher that looks over your shoulder.

MBK

As for layout, I used to start with the circuit and then run into problems with the seemingly trivial "rest".

Now my priorities are reversed. I would even go so far as to say the first thing to consider in a project is the enclosure. Next, the connectors and switches/pots, then the PSU. All the above are so expensive and individually different / hard to compare / assess, that experiments are almost out of the question for the average DIY'er. Also, their quality and effects on end result are usually ignored in application notes or textbooks.

Next in priority are grounding, and then the other connections from and to pcb - read, the interfaces. Here the parts are cheaper, and can be experimented with, but the subject is tricky. Interface design is an art I guess. Literature exists but is sometimes conflicting (grounding philosophies anyone?).

The circuit itself compared to the above is almost a piece of cake ;-). At least with the circuit the parts are cheap, can be easily experimented with on a breadboard, and many different types and solutions exist. The circuit can also be calculated and modelled. Try that with enclosures....

ALW

quote:

The circuit can also be calculated and modelled.

I'd agree with the former, although it's time consuming, but disagree with the latter, if using off-the-shelf models.

They'll tell you whether a circuit has a chance of working, but very little about it's real performance.

Anoyne modelled, for example, the PCB in their circuit?

Andy.

traderbam

I second MBK's three points and ALW's remarks.

In all my years of designing and listening and modifying and listening and making measurements using extremely expensive test gear courtesy of my last employer and then listening, one of the biggest lessons I've learned is that the cause of problems is usually simpler than you think. Being able to see the wood for the trees is the trick. And there are so many trees - all sorts of people are planting veritable forests all the time, often of complicated, ill-considered theories of relatively low importance.

Sometimes I think it is even more of a challenge for engineering graduates because many of the sweeping assumptions that work well in general electronics do not in audio and the graduate must discard years of learned assumptions and apply much more care and attention to unexpectedly important details.

The amateur is a easy victim of the profusion of academic papers and pseudo-amateur websites, which invariably are either too focussed on obscure and low priority items or contain much that is speculation disguised as fact. Which idea is most important? Who's opinion do you trust?

The good news in my experience is that audio design is a great leveller. You don't need a degree or a PhD to be the best. You just need to be able to think very clearly, believe that everything can be understood and always let your ears drive your theories.

IanHarvey

quote:

Originally posted by traderbam

In all my years of designing and listening and modifying and listening and making measurements using extremely expensive test gear

Talking about test gear, what do the panel consider essential bits of kit? I'd reckon instability problems are pretty impossible to track down without at least a scope, but what about more specialist bits of kit (distortion analysers and the like)?

Has anybody used PC-based audio analyser software (e.g. Sample Champion & the like)? Obviously, I assume a lot depends on the quality of your A-D/D-A.

Cheers
IH

Ian, you've poked a stick at my bete noir. When someone says that they want to design a speaker or an amp, but they haven't got a scope or FFT system, I just shudder. It's like saying, "I want to build a house, but I don't have a saw or a hammer."

Bare bones minimum:

Amps/preamps:
Analog voltmeter (having analog has saved my skin more than once!)
Digital voltmeter with high input Z
Scope, at least 2 channel, at least 20 MHz
Signal generator
Instrumentation amps
Bench power supplies

Speakers:
Calibrated test mike
FFT/MLS tester
Test amp and precision resistor (for Z measurements)
Pink noise source
Signal generator
1/3 octave spectrum analyzer

More equipment can be better (though best of all is the right equipment AND the know-how to use it properly). A willingness and ability to jury rig tests is essential. But this is the bare bones, the hammer and saw.

MBK

More tools make life easier, now to say what's truly essential... I guess a DVM, a Test CD, and a fast peak meter.

Actually a good Test CD probably comes before the scope, with a variety of signals that are for some reason hard to handle or where distortion is easy to hear.

Then in order of "making it easier":

a good and non-DIY reference system with AB or ABX switching functionality - to check what you're up against, to check "industry standard" (the competition). In my house now almost everything is DIY or tweaked (or so cheap and nasty that it's useless as a reference). That makes it hard to say anything because I can only talk about "before and after tweak".

scope

function generator

frequency analyzer

distortion analyzer

... yet often it's not the gross distortions that need analyzing - those can be heard, or guessed at (IC's getting hot...). What is most troublesome to measure is those intermittent problems, such as random pops and clicks, or transient distortions. How to measure that I don't even know.

The Elliot website has a couple of nice DIY test gear at http://sound.westhost.com/index.html .

mikek

quote:

Originally posted by MBK
... yet often it's not the gross distortions that need analyzing - those can be heard, or guessed at (IC's getting hot...). What is most troublesome to measure is those intermittent problems, such as random pops and clicks, or transient distortions. How to measure that I don't even know.

Intermittent bugs such as those you describe have a dispropotionate effect on the performance of your amp.....ergo......distortion residual must be time aligned with your output signal, and observed for some time with different resistive loads, including the reactive variety, or combinations thereof.

IanHarvey

quote:

Originally posted by traderbam
one of the biggest lessons I've learned is that the cause of problems is usually simpler than you think

How true. One of the dangers of relying purely on listening, without measurement or diagnostic aids, is that you never get down to why something sounded the way it did. Then you fall into the trap of attributing it to the first thing that comes to hand.

For example - selection of transistors in a differential input pair in a power amp. It's natural to try a few different types, find one that sounds good, and proclaim that type of transistor a Good Thing. However, it may be that that particular circuit relies on good matching between the input transistors (and isn't particularly sensitive to other parameters), and what you've actually done is stumbled across a well-matched pair by accident.

If so, taking the trouble to find this out will let you get good results from cheap transistors, and avoids you claiming things about transistor types which aren't reproducable elsewhere.

Cheers
IH

MBK

quote:

Originally posted by IanHarvey

How true. One of the dangers of relying purely on listening, without measurement or diagnostic aids, is that you never get down to why something sounded the way it did. Then you fall into the trap of attributing it to the first thing that comes to hand.

I agree to some extent but there is more to it IMO. Even with good measurement equipment you may still not be able to pin down why it sounded that way. Too many parameters to measure - which one did matter in some particular case? This falls again in the conundrum of finding out what matters most and what doesn't. Plus, there's those "measures bad - sounds good" cases.

To find out the parameters that the circuit is most vulnerable to I guess you need a mixture of theoretical intuitions and reasoning as to why this or that should matter most. Measurement can then confirm it. And for that good intuition the only thing that will help is broad background and broad experience. This is what I feel I miss the most in my own DIY fiddling.

Measurement alone can keep you busy forever if you don't have a good clue beforehand. That's what I mean with "to know what to measure and how to do it".

traderbam

Ian's example is an excellent one. It is really easy to draw the wrong conclusion from an observation. Considering many possibilities and testing out the simple ones first is a good methodology in my experience.

It is also critical to get the basics right before you attack the more complicated things. For example, you must get the grounding arrangements right at the start - otherwise you will spend your life messing with transistors and feedback systems and all sorts and get absolutely nowhere and become confused and frustrated because you can't find any consistency.

MBK is right that knowing what to measure and how to measure it requires a combination of experience and education and as such takes time to acquire. But you can work it out if you are diligent, systematic and learn and believe in basic engineering principles. Resist those who claim there is some etherial force at work that makes things sound good. No. Leave the art and esoterics to the musicians.

If you really want to achieve perfection I recommend starting with something extremely simple, something where the system is relatively simple and then play with it to gain intuition. The add to it in small steps and repeat playing with it. At each step try to understand what the engineering explanation is for the change in performance. Gradually build up the circuit and your knowledge.

If you start with someone else's complex circuit, like Slone's, you will find it very difficult to understand how to design things. The system is already very complex and changing a single component will not easily lead to a single cause of performance change. Rather, I would start with one transistor and a pair of headphones in class A and go from there. Use quality parts: polyester caps, tantalum electrolytics, metal film resistors - all easily available and quite adequate.

To start off with, you need to know Ohm's Law, you need to understand reactance and impedance, how to calculate power and how to calculate the static and dynamic currents in a circuit. If you use loop feedback you need to learn about stability. All of this can be gained from basic texts like Horowitz and Hill. Just one thing to note, an it's kind of important, very few electronics books deal with non-linearities and none deal with how non-linearities affect the sound of music. This is what you have to learn for yourself.

Beware of amateur publications: it is really hard to separate the wheat from the chaff, and beware of AES journal-like stuff because it is all about the academic pursuit of obscure concepts in excruciating detail. The very best source of info is the person who designed the amp you think sounds great - but guess what - they probably won't tell you 'cause they are making money in a competitive market and don't want to give away their hard-earned secrets.

MBK

quote:

Originally posted by traderbam
If you really want to achieve perfection I recommend starting with something extremely simple, something where the system is relatively simple and then play with it to gain intuition. The add to it in small steps and repeat playing with it. At each step try to understand what the engineering explanation is for the change in performance. Gradually build up the circuit and your knowledge.

Agree. Then again. So I started using op amp based circuits including the power stage to keep with systems where the design basics had been worked out by the manufacturer, right? Add water and mix, right? ... ... until ... ... until I realized that say "Understanding the inverting op-amp input" is not a textbook paragraph :rolleyes: ... but a book!! ... in 35 volumes!!!

:bawling:

At this point I'd be happy enough if I truly understood what maketh a decent power supply.

[note: It's a joke. A joke! Errr. Not.] :scratch:

Fred Dieckmann

"Beware of amateur publications: it is really hard to separate the wheat from the chaff, and beware of AES journal-like stuff because it is all about the academic pursuit of obscure concepts in excruciating detail. The very best source of info is the person who designed the amp you think sounds great - but guess what - they probably won't tell you 'cause they are making money in a competitive market and don't want to give away their hard-earned secrets."

Other than the fact that some of the greatest articles on audio design were written for the Audio Amateur by Nelson Pass, Erno Borbely, Richard Marsh, Walt Jung, Ben Duncan, and our own DIY member Jan Didden. Many of these articles were written by people outside the audio industry with new approaches and test equipment outside the realm of the standard audio test equipment used by most designers. It's kind of hard to layout the cash for things like a $60 K network analyzer. I had access to an Agilent 4284A Precision LCR Meter at my last telecom job that was quite useful but was about $15 K. I was so sad to see my test equipment and I part company that I could have written a country western song about it that would make any engineer cry.

Knowledge of topologies, passive components, and listening to what other designers are doing is essential but the good fundamentals of engineering will take you to the point and beyond that the tweeker will reach and in less time.
Skills and experience in both camps are very useful. Perhaps a new term like EnginEARing is in order to describe the combination of the two approaches.......

Fred

P. S. Nelson and Erno are sharing secrets like mad. A removed top and 30 minutes with a good amplifier will also tell you a hell of a lot, but don't Steve McCormak or he will start potting things or removing part numbers.

Fred Dieckmann

"observed for some time with different resistive loads, including the reactive variety"

I would like to see one of those! My friend Jay O. Mega says it would be too complex for me and resisted telling me why for some reason. I will not be impeded and will get the angle on this no matter what the magnitude of the task. I thought you were serious until I read the post again but some of the other stuff gave it away as subtle example of techno-humor. I'm jealous even with the number of times that I posted humor that was taken for actual advice. I tip my hat to you and will endeavor to work harder in the face of such competition.

http://www.wordspring.com/yogiberaquotes.html variety"

Good one,
Fred

traderbam

I empathize, MBK.
The op-amp is a classic example of a very complex circuit which mfrs portray as very simple. Op-amps are not usually designed for audiophile applications, nor are they usually designed by experienced audio designers. Mfrs make most of their money by selling these things to other industries, where parameters like power consumption, power bandwidth, stability, noise, reliability, price, size, availability are primary motivators.

So the amateur should not make the mistake of believing something is fit for purpose just because it is made by a respected name in the components industry.

Besides, in order to reduce size and manufacturing cost, opamps are made on a wafer of silicon. Recall that silicon is a semi-conductor and thus is inherently NON-LINEAR. This means resistors in an opamp will be inferior to discrete carbon or metal film resistors. Similarly, silicon capacitors are non-linear and cannot be made very large due to wafer realestate consumption - only tens of pF. Try regulating a circuit with just a few pF to play with. Inductors are almost impossible to make in silicon wafers without huge area consumption and so they are avoided. You have no control over the matching of parts within an op-amp.

The good aspects of opamps is that they are small - reducing inductance - and certain performance parameters are fairly tightly controlled or tested-in by the mfrs. It is easy to make a functioning circuit first time because you have less components to deal with and connect up.

quote:

Other than the fact that some of the greatest articles on audio design were written for the Audio Amateur by Nelson Pass, Erno Borbely, Richard Marsh, Walt Jung, Ben Duncan, and our own DIY member Jan Didden.

There's also a LOT of chaff. Say, was it Marsh who wrote that article about shunt regulators in AA with a design that didn't/couldn't work? I remember a follow up article from someone who pointed out the fatal flaws (no feedback, no series resistance). Marsh's response was something to the effect of, "Well, MINE worked, but I've lost all my notes on it."

Jan's regulator designs were first-rate.

traderbam

quote:

Sure Fred. At the risk of hardened arteries I would, nonetheless, take all of these sources with a pinch of salt and scrutinize their theories in the context of your own circuit.

Fred Dieckmann

"Op-amps are not usually designed for audiophile applications, nor are they usually designed by experienced audio designers. Mfrs make most of their money by selling these things to other industries, where parameters like power consumption, power bandwidth, stability, noise, reliability, price, size, availability are primary motivators."

This is too much....... There is really not that much in priciple for a well designed op amp not to be good for audio. John Curl holds Scott Wurcer at Analog Devices to be a serious audio geek and says he has built discrete J fetss designs for his home audio system. Scott has designed some of ADs most interesting Op amps

From the OPA604 data sheet:

The OPA604 is a FET-input operational amplifier designed for enhanced AC performance. Very low distortion, low noise and wide bandwidth provide superior performance in high quality audio and other applications requiring excellent dynamic performance."

Go pull the top off a DVD player and tell me what logo you see on the op amps and how many, and tell me the audio market place is not a significant customer. Many of the op amps are quite good now and sonically bettered by someone with extremely good design skills in discrete design. I design with both approaches depending on the application.

Is it the British counterpart for April fools day today or something?

Fred Dieckmann

quote:

Originally posted by SY

There's also a LOT of chaff. Say, was it Marsh who wrote that article about shunt regulators in AA with a design that didn't/couldn't work? I remember a follow up article from someone who pointed out the fatal flaws (no feedback, no series resistance). Marsh's response was something to the effect of, "Well, MINE worked, but I've lost all my notes on it."

Jan's regulator designs were first-rate.

I remember the circuit and error but I don't remember that response.......... I do seem to remember the fix being sent in by someone. Oh by the way Dick Marsh is a highly successful high end audio designer today with favorably reviewed designs and is well respected by a few designers I have talked to. I guess he over came that design problem.

It seemed to me to be a schematic error and an obvious one at that to me and a several others, and not a real design flaw. It is an easy thing to do and a lot of stuff is built before the schematic is drawn. I found a schematic error on a telecom board a couple of years ago (non and inverting op amp inputs swapped) and every one swore it couldn't happened with design reviews, computer data bases for the schematic and PCB layout and the board was working for god's sake! They said I must be mistaken. Other than the fact that I know how an op amp works......... The pulled a board from the lab and ohmed it out and guess what.......... the schematic was wrong. Guess what I have seen a circuit in several op amp application data sheets that both Nelson Pass and I scratched our heads over. I thought it should work he didn't. I ran Spice and Nelson was right. I found the original circuit and it included coupling caps the op amp version. If I give you the info will you call Analog Devices and tell them its wrong and tell me what they plan to do about it?

http://www.marshsounddesign.com

He also originated the MIT multicap. I can't say much for his taste in shirts though..........

http://www.marshsounddesign.com/contactset.htm

traderbam

quote:

It seemed to me to be a schematic error and an obvious one at that to me and a several others, and not a real design flaw.

Well, the follow up (a full article, not a correction) appeared in AA 4/88, p46 (John Adelsbach, "Push-Pull Shunt Regulator Revisited"). The entire concept of the regulator was flawed- it wasn't a simple schematic mistake, unless that schematic mistake coincided perfectly with circuit board mistakes. Marsh claimed that the prototype worked, but was unable to provide any documentation or the prototype itself.

ALW

quote:

And the need for low power consumption specs leads to the use of class B circuits.

Has anyone realised the patent for the Quad 'current dumping' feed-forward correction system first used on the 405 is due to expire this year (or has already?).

If there was an output stage topology that should be ideal for DIY, this could be it. I have a sneaking suspicion it never quite realised it's full potential in Quad's hands.

Andy

Fred Dieckmann

You are dissappointing me now Fred.

You are doing just what I said you shouldn't: taking the datasheet as read. And what evidence is there of the sound quality of Scott Wurcer's home brew amps? Interesting that he is designing his amps using discrete parts.

Having just looked at the datasheet (on the web) there isn't much I can tell about the audio performance of the OPA604. "

I don't what in particular you are referring by 'taking the data sheet as read." I assume you mean thinking the ap note circuit worked initially. At first inspection and with some simple nodal analysis it appeared to and with the coupling caps it would. I ran a Spice model and got the same results as Mr. Pass as to the problem. I was also curious enough to find the original design to see why the circuit had been included and where they went wrong.

I have never seen a Class B stage in any op amp and for most typical loads in a preamp they are class A or class AB. 5 volts into 10K is 0.5 mA and far below the bias current of most op amps used for audio. The AD 825 is biased at bout 6.5 mA and the open loop output impedance is 8 ohms indicating a good amount of bias through the out put stage. The AD811 has a supply current of 16.5mA at +/- 15 volts and requires a heat sink at these voltages. It is often used as an output stage in composite op amps.

Scott Wurcer has designed several very good sounding op amps, has the respect of John Curl, and might design with jfets at home
because he is tired of playing with op amps at work. How many of you do for a hobby what you do for work? I would be quite happy to take design audio advice from him. Someone who can design op amps must know enough to design great discrete circuits. The converse is probably not true very often. The demands for low distortion and low DC offsets and drift are orders of magnitude better than many discrete designs can deliver due to the thermal coupling and close transistor matching of several transistors fabed on the same die. It is difficult with a discrete transistor design to get above a few tens of MHz before board parasitic will give you major headaches. i have seen op amp with gain bandwidth product of a GigaHertz!

The real exploitation of the virtues and minimization of the drawbacks backs of op amps comes from composite circuits. The first in loop external output stage I ever saw was the use of a jfet follower with jfet current source inside the feedback loop of an op amp. This was done by PS audio maybe 15 years ago. I have seen tubes, mosfets, bipolar transistors, video op amps inside the loop of op amps. Op amp based power supplies have been in tube amps and preamps for about 20 years and even used in some Audio Research tube products. I have lost count of the number of op amp based servos to DC couple discrete transistor designs.

I design with discretes but writing off op amps with the level of design and new composite circuits in use would be very foolish
and may be at the point where op amp based designs with enough attention to details could be better than many less rigorously discrete designs. Jocko and I were just looking at some of the new jfet op amp data sheets and notice the specs for even the non exotic designs would be state of the art a few years ago. The last five years have seen some amazing improvements to op amps and op amp circuits and a serious audio designer would ignore them at his peril since the gap is rapidly narrowing.

IanHarvey

quote:

Originally posted by traderbam
All silicon circuits really do constrain the designer. And the need for low power consumption specs leads to the use of class B circuits. You'd think the ultimate op-amp would at least be single-ended class A.

You can of course bias an op-amp output into class A by pulling up (or down) the output with a suitable resistor (or constant current source), although I imagine this might unbalance the inputs a bit.

Cheers
IH

Fred Dieckmann

quote:

Originally posted by ALW

Has anyone realised the patent for the Quad 'current dumping' feed-forward correction system first used on the 405 is due to expire this year (or has already?).

If there was an output stage topology that should be ideal for DIY, this could be it. I have a sneaking suspicion it never quite realised it's full potential in Quad's hands.

Andy

I have heard the tweaked version by the talented Steve McCormack and it still failed to reach much potential........ despite some very good press on the modded version as I remember.

quote:

Scott Wurcer has designed several very good sounding op amps, has the respect of John Curl, and might design with jfets at home because he is tired of playing with op amps at work. How many of you do for a hobby what you do for work? I would be quite happy to take design audio advice from him.

Scott Wurcer has no bigger fan than me, not the least for his habit of opening Burgundies that I can't afford. You might not like many of his views about "high end" audio. But he does have some hilarious anecdotes, most of which would get me sued if I repeated them.

traderbam

quote:

I design with discretes but writing off op amps with the level of design and new composite circuits in use would be very foolish

I agree. And I agree with class A/AB in the case of low-I circuits.
How about power op-amps? What level of performance is state of the art these days?

millwood

quote:

Originally posted by Fred Dieckmann
I have never seen a Class B stage in any op amp and for most typical loads in a preamp they are class A or class AB.

wouldn't that depend on how you define those classes? To me, a class B is a circuitry that conducts 180 degrees, and class C <180 degrees. Class AB to me is one that is originally class A for small signals but gets pu